<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .father {
            width: 100px;
            height: 100px;
            background-color: red;
            padding: 10px;
        }
        .father .son {
            width: 50px;
            height: 50px;
            background-color: blue;
        }
        .son.xixi {
            color: pink;
        }
    </style>
</head>
<body>
    <div class="father">
        fefgregfge
        <div class="son xixi">发的发</div>
        <div class="son">fefg </div>
        <div class="xixi">fefefrrtgtrg</div>
    </div>
</body>
</html>